Playlists and collections are different things. Playlists are basic list with no metadata, just add/remove. Collections have their own metadata and managing this from other Play clients like the iOS app would require a lot of effort. Not saying it won’t be possible in the future, but there are no immediate plans to bring admin features like this to other Plex clients.
There’s already a feature request so you can add your vote there, Administration from mobile devices.
